Page 393 - IRSEM_Main Book

17.4.2 Installation and Maintenance of AFTC

(a) Installation of track circuit shall strictly follow the instructions given for that
type of track circuit.

(b) Tuning area shall be devoid of check rails, level crossing, insulated bond
and each fish plated joint shall be bonded with jumpers of adequate
thickness.

(c) Special precautions shall be taken to ensure the tightness of connection of
rail and tuning unit.

(d) A frequency assignment scheme for the track circuit shall be decided in
advance and it shall be strictly followed.

(e) Terminal junction on insulation joint to track circuits with the same
frequency is prohibited; however, frequencies not belonging to same pair
can be used.

(f) Cable cores of same cable shall not be used for connecting transmitter &
receiver of a track circuit.

(g) When wiring and installing track circuit, circuit pairing should be observed in
the line cables. Each transmission or reception shall use conductors from
one same pair. Circuit pairing results in cable transmission parameters
being changed and may induce significant cross talk levels in adjacent
circuits.

(h) The design and installation of field equipments should take in account the
requirements for mechanised track maintenance and should not be hazard
for men walking along the track.

(i) Protection against atmospheric voltage surges shall be installed on each
pair of conductors providing a link to the outside in order to limit the harmful
effect of lightening on electronic equipment. This protective arrangement
shall cover against both common mode and differential mode voltages on
line.

(j) Transmitter, receiver and power supply shall be mounted in standard relay
rack in a manner to allow maintenance and testing staff to view the track
relay while making adjustments.

(k) TUs and ETUs shall be mounted at a minimum distance of two meters
away from the near rail as it gives good safety margin to staff.

(l) In case of failure of track circuit, attempt shall not be made to pick up the
track circuit by adjusting the gain of receiver of TC without investigating the
cause of drift in the receiver voltage.

(m) Impedance bond within track circuit shall be tuned with the correct
resonating capacitor across the auxiliary coil and this tuning shall match
with the frequency of track circuit.

Chapter 17: Train Detection Track Circuits & Axle Counters Page 341 of 535